1. Field of the Invention
The present invention relates to a snubber circuit for suppressing a voltage ringing at a time of a turn-off of a switch element and a power transformer such as a switching power supply, using the snubber circuit.
2. Description of the Related Art
Examples of power transformers include switching power supplies of both insulated types using a converter transformer and non-insulated types using no converter transformer.
In both types of switching power supplies, a switch element experiences sudden voltage changes (a voltage ringing phenomenon) at a time of a turn-off of the switch element due to a leakage inductance of a choke coil or a primary coil of the converter transformer.
A snubber circuit is provided for mainly suppressing the voltage ringing.
The voltage ringing at the time of the turn-off of the switch element is especially large if the switching power supply has the large leakage inductance in the primary coil of the converter transformer. Therefore, it is preferred that the snubber circuit can suppress the voltage ringing more efficiently.
However, when the leakage inductance is large, suppressing voltage ringing with a conventional snubber circuit has resulted in huge power loss.
Accordingly, a primary object of the invention is to provide a snubber circuit capable of efficiently suppressing a voltage ringing at a time of a turn-off of a switch element while keeping an energy loss to a sufficiently low level.
Other objects, features, and advantages of the invention would be obvious from the following description.
The present invention is, in summary, a snubber circuit provided in a power transformer including at least: a switch element for operating for a power transformation control; a magnetic substance for a storing and releasing energy in relation to power transformation accompanying with an operation of the switch element; and a commutating diode for conducting by means of the energy stored in the magnetic substance, the snubber circuit including: a first series circuit composed of a capacitor and a diode connected in series; and a second series circuit composed of a coil and a diode connected in series, wherein the first series circuit is connected in parallel with the commutating diode in a state that the capacitor is connected to the magnetic substance side in the commutating diode; and the second series circuit is connected between a connecting portion between the capacitor and the diode in the first series circuit and a commutating diode non-connecting side in the magnetic substance.
The power transformers mentioned above include not only switching power supplies, but also other kinds of power transformers such as inverters.
The switch elements include not only switching transistors such as bipolar transistors and MOS transistors, but also other kinds of switch elements.
The magnetic substance mentioned above include any magnetic substance such as a secondary coil of a transformer, a choke coil and other magnetic components, which stores and releases energy as a result of operation of a switch element.
The commutating diodes include diodes which conduct by means of stored energy of a magnetic substance, for example, a rectifying diode disposed in the secondary side of a transformer in a flyback switching power supply and a commutating diode in the secondary side of a transformer in a forward switching power supply.
In the first series circuit, the capacitor and the diode include any aspects connected in series whether directly or indirectly.
An aspect in which the first series circuit is connected to the commutating diode in parallel includes any aspects connected in parallel whether directly or indirectly.
An aspect in which the capacitor within the first series circuit is connected to the magnetic substance connecting side in the commutating diode includes any aspects connected to either an anode side or cathode side of the commutating diode whether directly or indirectly.
A connecting portion of a capacitor and a diode in the first series circuit includes any aspects in which the capacitor and the diode connected whether directly or indirectly.
In the second series circuit, the coil and the diode include any aspects connected in series whether directly or indirectly.
An aspect in which the second series circuit is connected to a commutating diode non-connecting side in the magnetic substance includes any aspects connected to the commutating diode non-connecting side of the magnetic substance whether directly or indirectly.
In accordance with the snubber circuit of the invention, in a state that the energy is fully stored in the capacitor of the first series circuit, when the switch element is turned off, since the stored energy of the capacitor is released through the magnetic substance, an electric current of the switch element doesn""t rapidly become smaller, but gradually becomes smaller.
Consequently, the voltage ringing at a time of a turn-off of the switch element is suppressed.
In this case, even if the coil used for power transformation in a switching power supply employing a converter transformer, the switching power supply employing a tapped inductor and the like has a large leakage inductance, since a component is formed by a capacitor, diode and coil, enhancing voltage ringing suppression effects does not cause power loss.
As mentioned above, according to the invention, the voltage ringing at the time of the turn-off of the switch element can be suppressed while considerably suppressing the power loss.
A power transformer in accordance with the invention, includes: a switch element for operating for a power transformation control; a magnetic substance for storing and releasing an electrical energy in relation to the power transformation that accompanies operation of the switch element; a commutating diode for conducting by means of the stored energy of the magnetic substance; and a snubber circuit for suppressing voltage variations at a time of a turn-off of the switch element, wherein the snubber circuit has a first series circuit of a capacitor and a diode and a second series circuit of a coil and a diode, the first series circuit is connected in parallel to the commutating diode in a state that the capacitor is connected to a magnetic substance connecting side in the commutating diode, and the second series circuit is connected between a connecting portion of the capacitor and the diode in the first series circuit and a commutating diode non-connecting side in the magnetic substance.
According to the power transformer in accordance with the invention, since the snubber circuit is used, a suppression of the voltage ringing at the time of the turn-off of the switch element and a power loss accompanying the suppression thereof can be considerably reduced.